6 replies to this topic

[ChrisA]

How does the by-pass pressure of an oil filter correlate to the oil pressure reading we see on gauge? Basically, if a filter says it's by-pass pressure is 11-17 psi and the oil pressure we see gauge at the sensor indicates a much higher pressure, does that mean most of the oil is by-passing the filter element?

[Keith Andrews]

I'll take a stab at it and say no. I think it would depend on where you are reading the pressure. That is a WAG though.

[KentCarter]

http://www.aftermark...lish/88-3R2.pdf

It looks like the by-pass pressure specification relates to pressure from side of the filter element to the other. So, it would not relate directly to the gauge pressure. When the engine oil is cold and oil doesn't want to pass easily through the element, the bypass valve is more likely to be open, especially as flow increases. Of course, the oil pressure is high during warmup due to bearing clearances. The diagrams I have seen shows the oil-pressure sender port to be post filter, so the resistance of the filter element isn't increasing the gauge pressure.

[ChrisA]

http://www.aftermarketsuppliers.org/Councils/Filter-Manufacturers-Council/TSBs-2/English/88-3R2.pdf

It looks like the by-pass pressure specification relates to pressure from side of the filter element to the other. So, it would not relate directly to the gauge pressure. When the engine oil is cold and oil doesn't want to pass easily through the element, the bypass valve is more likely to be open, especially as flow increases. Of course, the oil pressure is high during warmup due to bearing clearances. The diagrams I have seen shows the oil-pressure sender port to be post filter, so the resistance of the filter element isn't increasing the gauge pressure.

Yes, the Miata's pressure port is post filter. That would make me believe that if the filters by-pass valve were to fail we would see a lower pressure on the gauge when cold or if the filter were clogged. I know CM and Wix Racing filters have much higher rates than standard filters and some incorporate no by-pass valve. However, Wix does not have one that will fit the miata and the CM is way expensive. I also don't know how small of particles they filter. Would be interesting to know what the correlation is between the pressure the filter opens at and what we read on gauge. Are we getting full filtration at 7000-rpm or are we by-passing a lot of oil?

[Dennis]

Is there any reason not to use the Mazda filters from Mazdaspeed? Convenient to throw on any order and only $5.

Dennis

[FTodaro]

Is there any reason not to use the Mazda filters from Mazdaspeed? Convenient to throw on any order and only $5.

Dennis

i think so, this year I used a Bosch 3323 its really for a honda civic, I found this out as my daughter has a civic and i grabbed the wrong filter as I headed to the track and found that it fit. it has about 70% more volume that the Mazda filter its huge. I am thinking of switching to the Wix filter because I think it is better constructed and it uses a natural fiber filter and the Bosch uses a synthetic filter which I am not sold on. so the biggest reason is a larger canister and better paper. The Bosch pressure valve pops between 14 to 18 psi and the wix is 8 to 11 and I have been trying to figure out it this is a distinction with a difference.

[Dennis]

So size does matter! It makes sense that a bigger filter can have a greater surface area and can catch more stuff before plugging up and opening the bypass. Anyone know the relief valve pressure for the Mazda filter? Does it have one? Do all oil filters have a relief valve?

I have been comfortable using the Mazda filter since I use really good synthetic oil (RedLine) and change oil and filter often (every 2 weekends at most). Anybody have a bad experience they think was caused by the filter?

Dennis